This invention relates to new and useful improvements in coupling assemblies for breakaway pole bases.
In my previous Canadian Pat. No. 973,677 and U.S. Pat. No. 3,837,752, (incorporated by reference) I disclosed a coupling for the attachment of poles to a base such as a concrete base and adapted primarily for use with free standing utility poles such as roadside lighting supports.
The coupling disclosed in the above patents includes a plurality of breakaway or frangible coupling bolts attachable to existing bolts extended upwardly from the conventional concrete base and adapted to receive the base plate of the utility pole. These couplers are designed to fracture in the event that an impact is received by the pole along a line substantially parallel to the base such as would be the case if a vehicle struck the pole. Such lateral impact loads produce bending in the couplers. Hence, the impact resistance of the couplers is determined by their design bending strength.
It is desirable to have low bending strength in order to serve the purpose of frangible pole bases.
At the same time, normal operating wind and static loads produce primarily axial loads in the couplers. Hence the normal operating strength of the couplers is determined by their design axial strength. However, in poles with long unbalanced davit arms, normal wind loads produce torsion in the pole and, hence, bending in the couplers. Thus, in this case, the normal operating strength is limited by the bending strength of the individual couplers in which, as noted above, it is desirable to have low bending strength.